A. It is very possible that she is developing a hip condition (hip dysplasia), it is a very common condition in older big dogs and is also related to age and weight. It could also be some other kind of arthritis, and cold usually makes arthritis worst. If she keeps on like this you will need to go to the vet, she might need anti inflammatories at least for a short while.
A. Arthrosis and arthritis usually get wear during winter / cold weather. Hip arthritis is a major differential in her case.
I would recommend to Take her to your veterinarian for a check up and possibly some pain relief/ antiinflammatories medications. Radiographs would help to identify signs of arthritis/ arthrosis.
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